The present invention relates to a composition for preventing and improving metabolic syndrome utilizing soy germ protein, more specifically to a composition for improving the blood lipid condition and the blood sugar level, controlling the increase in liver weight, and reducing the body weight.
In Japan, from ancient times, soybeans have been eaten in various forms, such as bean curd, soybean milk, deep-fat fried bean curd, boiled beans, fermented soybeans, soybean flour, miso (fermented soybean paste), and soy sauce. In recent years, various physiological components are receiving attention, so that soybean is expected to serve as food useful for health maintenance. Soybean protein (defatted soybean), which is prepared by removing oil from soybean, contains about 40 to 50% protein, and has relatively good amino acid balance of a vegetable protein. Therefore, soybean protein is called “field meat”, and widely used for food and feed applications. Functional components contained in soybeans, such as isoflavone, lecithin, and vitamin E are also receiving attention, and these useful components have been used as supplements for, for example, prevention of various diseases. However, soybeans also contains a trypsin inhibitor which inhibits the activity of proteolytic enzymes, an antigenic protein as an allergen which causes an allergy, phytic acid which inhibits absorption of minerals and the like. Effective use of soybean as a nutritional functional food is based on two main points of efficient use of useful components and reduction of antinutrient components.
On the other hands, in recent years, metabolic syndrome has become a significant public health issue particularly among people of middle and advanced age, and food and drugs for improving the syndrome have been demanded. It is well known that soybeans reduce the blood cholesterol level. The effect is likely due to that soybean protein specifically binds to cholesterol precursors such as bile acid, and is excreted as feces.
In order to investigate the physiological functions such as the cholesterol reducing effect, identification of functional fractions of peptide components obtained from decomposed soybean protein has been studied. For example, it is confirmed that undigested fractions obtained by enzymatic digestion of soybean protein lower the cholesterol level (Patent Document 1, Non-patent Documents 1 and 2). As other soybean components which improve the blood neutral lipid, cholesterol and blood sugar levels, 11S globulin called glycinin (Patent Document 2), 7S globulin called β-conglycinin, isoflavone, and others are said to be effective, but no clear conclusion has been provided. Further, proteins of soybean germ have little been studied.
Regarding the substances derived from soybean germ, it is reported that isoflavone aglycon, which is contained in a substance prepared by treating soybean germ with aspergillus oryzae, hydrolyzing the product, and extracting and concentrating the product with a solvent, is effective as an active ingredient for promoting bioactivity (Patent Document 3). However, there still are different opinions among researchers about the efficacy of isoflavone inclusive of its metabolites, so that no clear conclusion has been provided.
The protein composition of soybean germ is markedly different from that of soybean. Soybean germ has a low nutritional value because it contains little storage protein such as conglycinin and β-conglycinin, and its total protein content is low. In addition, soybean germ abundantly contains antinutrients such as saponin and allergens, so that its excessive ingestion causes an allergy, growth inhibition or the like. Soybean germ further has a bad flavor. Therefore, it is believed to be unsuitable for uses in foods, beverages, and medicines. The inventors have applied for a patent on a soybean germ protein composition which resolves the problem (Japanese Patent Application No. 2005-36942). The composition is prepared by removing antinutrient components from soybean germ through solvent treatment in combination with heat treatment. The process increases the content of soybean germ protein while decreasing the content of allergens derived from the protein, and improves the flavor. However, functionality of soybean germ protein, more specifically, processing characteristics and physiological effects caused by the ingestion of the protein have not known at all until the completion of the present invention.    Patent Document 1: Japanese Patent Publication No. 07-025796    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-88334    Patent Document 3: WO 2003/077904    Non-patent Document 1: Atherosclerosis, 72, 115, 1988    Non-patent Document 2: J. Nutr., 120, 977, 1990